Heart failure (HF) is an important clinical problem and abnormalities in cardiac myocyte (CM) calcium (Ca) handling make a significant contribution to contractile dysfunction. Increasing the activity of the Ca ATPase of the Sarcoplasmic reticulum (SERCa2) in hearts with pressure overload (PO) induced cardiac hypertrophy (CH) and decreased contractile function improves the Ca transient and leads to enhanced contractile performance. The long-term positive or negative consequences of conditional increases in SERCa2 activity at different stages of cardiac hypertrophy and heart failure (HF) are however unclear. In aim I, we will determine the long term positive or negative consequences of increasing SERCa2 activity in a conditional, inducible fashion to enhance the delayed diastolic Ca transient in hearts with PO induced HF. Our preliminary results indicate that increasing SERCa2 activity in PO mice with overt HF, may further curtail a limited energetic supply and impair work output. We will explore if increasing SERCa2 activity in a conditional, timed manner in hearts with different degrees of CH and HF can still improve the Ca transient and contractile function. Adeno associated virus based transgene delivery and transgenic animals allowing for tetracycline system or Cre LoxP based "stuffer" removal with conditional increases in SERCa2 activity are used. Abnormal Ca handling and contractile function in CH/HF hearts may be in part mediated by decreased sarcoplasmic reticulum (SR) Ca loading due to an increased diastolic Ca leak. In aim II, we will explore mechanisms to diminish the SR Ca leak using potentially ryanodine receptor interacting proteins like Sorcin, FKB12.6, and Homer1c. Our preliminary show significant positive effects of FKBP12.6,Sorcin on SR Ca loading. In aim III, we will pursue our preliminary findings that mitochondrial (Mito) Ca flux is abnormal in CM obtained from failing hearts and determine the underlying mechanisms. We will also pursue our preliminary results that Sorcin localizes to mitochondria and markedly improves abnormal Mito Ca handling. In addition, we will determine if HF induces changes in Mito Ca handling is correlated with diminished high-energy phosphate production and can be reverted towards normal. [unreadable] [unreadable] [unreadable] [unreadable]